Process for producing vinyl polymers

ABSTRACT

The present invention relates to a method of radical polymerization of a vinyl monomer in the presence of a hydroxylamine. Specifically, the invention provides a process for producing a vinyl polymer having a controlled molecular weight range and a controlled level of polydispersity.

This application is a continuation of Ser. No. 09/026,745 filed Feb. 20,1998 now U.S. Pat No. 6,242,546. This application claims foreignpriority benefits under Title 35, United States Code, Section 119, toJapanese patent application number 9-56933 filed Feb. 24, 1997. Each ofthese applications are expressly incorporated herein in their entiretyfor all purposes.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of radical polymerization of avinyl monomer in the presence of a specific substance, and particularly,to a process for efficiently producing a vinyl polymer which has a highmolecular weight desirable for practical properties such as mechanicalproperties, heat resistance and the like, and which has controlledmolecular weight distribution.

2. Description of the Prior Art

In conventional radical polymerization, the molecular weight of theproduced polymer strongly depends on the polymerization temperature,that is, the molecular weight of the polymer obtained is restricted bythe polymerization temperature. Although the polymerization temperatureis typically lowered in order to achieve a high molecular weight,decrease in polymerization temperature will elongate the polymerizationtime and increase the amount of remaining monomer. It becomes,therefore, difficult to effect an efficient production. Similarly,although the polymerization temperature is typically elevated in orderto achieve a low molecular weight, increase in polymerizationtemperature will so accelerate the polymerization rate that it becomesdifficult to control the reaction. For these reasons, there is a wideneed for a polymeriztion method of freely controlling the molecularweight in a radical polymerization.

As an attempt to control the molecular weight in a radicalpolymerization, Tatemoto et. al. have reported that radicalpolymerization of a fluorine-containing monomer such astetrafluoroethylene proceeds in a manner like living polymerization inthe presence of an iodine compound such as CF₃)₂CF-I (Shozo Tatemoto,Koubunshi-Ronbum-Shu, 49, 765 (1992)). Likewise, Otsu et al. have foundthat, when certain sulfur compounds were used, radical polymerization ofstyrene or the like occurred under light irradiation and that the extentof conversion and the molecular weight of the produced polymer increasedwith the time (J. Polym. sci.; part A; polym. chem., 32, 2911 (1994)).According to these methods, it is possible to control the molecularweight in a considerable wide range. However, these methods lackuniversality because they require a special polymerization initiator ora use of limited kinds of monomer.

In anionic polymerization, a precise control of the molecular weight ispossible by a polymerization method called living polymerization.Recently, it has also become popular to research a polymerization systemwhich enables living polymerization in radical polymerization. Forexample, it has been shown in Japanese Patent Publication No. 94-199916A that, by using a radical polymerization initiator such as benzoylperoxide together with a stable free radical agent such as2,2,6,6-tetramethyl-piperidinyloxy (TEMPO), a living-like polymeriztionof styrene can be achieved. According to this method, by selecting apolymerization condition, the molecular weight of the polymer obtainedwill depend not only on the polymerization temperature but also on theamounts of the initiator and the stable free radical agent used, so thatone can control the molecular weight by those amounts to a certainextent.

Thus, when the above method is used, one can obtain a resin having acontrolled molecular weight. However, this method has a drawback thatthe reaction rate in this method is so slow that it takes considerablymore time compared with the usual radical polymerization to reach a highextent of conversion. In addition, coloration of the obtained polymermay sometimes occur depending on the reaction condition. Furthermore,TEMPO requires special attention in its handling and storage because itexists in radical state, and it is also very expensive. This methods hasthus some shortcomings that, for example, it requires more productioncosts compared with the conventional methods.

In view of such a situation, the present inventors have concentratedtheir efforts on controlling the radical reaction of vinyl monomer withthe aim of increasing productivity and improving practical physicalproperties of radically polymerized vinyl polymers. In result, we havefound by chance a method for obtaining a vinyl polymer having a highmolecular weight and a restrained molecular weight distribution whileretaining a high polymerization rate by including a specific substitutedalkylhydroxylamine in the polymerization system, and thus completed thepresent invention.

SUMMARY OF THE INVENTION

The present invention provides a process for producing a vinyl polymercharacterized in that, in a radical polymerization of a vinyl monomer, asubstituted hydroxylamine represented by a general formula:

(in which R₁ and R₂ represent hydrogen, a (substitued) aliphatichydrocarbon group having one or more carbon atom(s) or an aromatichydrocarbon group) and/or a general formula:

(in which R₃ and R₄ represent a (substitued) aliphatic hydrocarbon grouphaving one or more carbon atom(s)) is added.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is described below in more detail.

In each of R₁ and R₂ of the general formula (1) of the presentinvention, the aliphatic hydrocarbon group may include, for example,methyl, ethyl, isopropyl, t-butyl, butyl and the like group, and thearomatic hydrocarbon group may include, for example, phenyl, benzyl andthe like group.

Similarly, —R₃—R₄— in the general formula (2) may include a divalent(substituted) aliphatic hydrocarbon group corresponding to those groupsin the general formula (1) such as —CH₂CH₂—, —CH₂CH₂CH₂CH₂—,—CH(CH₃)CH₂—CH(CH₃)CH₂—, —C(CH₃)₂CH₂—C(CH₃ ₂CH₂—,—CH₂CH₂CH₂CH₂—CH₂CH₂CH₂CH₂—, or the like.

Furthermore, the hydrocarbon groups in the above general formulas (1)and (2) may optionally be substituted, and the substituent may include,for example, an aliphatic hydrocarbon such as a methyl or ethyl group,an aromatic hydrocarbon such as a phenyl group, halogen, a halogenatedhydrocarbon, a carbonyl group, a hydroxy group, an amino group, and thelike.

In the present invention, the substance represented by the generalformula (1) (substituted hydroxylamine) may includedimethylhydroxylamine, diethylhydroxylamine, isopropylhydroxylamine,dibenzylhydroxylamine and the like.

In the present invention, the substance represented by the generalformula (2) may include N-hydroxylamaleimide, N-hydroxylsuccinimide,N-hydroxylphtalimide and the like.

In the present invention, although the radical polymerization may beinitiated by any of the known methods, for example, using an initiator,heat, light or radioactive rays, it is preferable to use an initiator.Although there is no special restriction on the ratio of the substancerepresented by the above general formulas(1) an (2) (substitutedhydroxylamine) used to the radical polymerization initiator, it ispreferable to use a mole ratio between the substance represented by theabove general formulas(1) and (2) and the radical polymerizationinitiator at 0.01/1-100/1 (substance represented by the above generalformula(1) and (2) [substituted hydroxylamine]/radical polymerizationinitiator), more preferably at 0.1/1-10/1, and particularly preferablyat 0.11/1-1.0/1. At a mole ratio of the substance represented by theabove general formula (1) and (2) to the radical polymerizationinitiator below 0.01/1, it will be difficult to control the molecularweight and molecular weight distribution, while at a mole ratio above100/1, the polymerization rate will decrease.

There is a no special restriction on the vinyl monomer used in thepresent invention, and it may be exemplified by aromatic vinylcompounds, α, β-unsaturated carboxylic acids, α,β-unsaturated carboxylicacid esters, α,β-unsaturated carboxylic amides, α,β-unsaturatednitriles, vinyl carboxylates, vinyl halides, vinylidene halides,conjugated dienes and the like compounds capable of radicallypolymerizing.

As an aromatic vinyl compound, although styrene is typically used, otheraromatic vinyl compounds, for example, an alkyl-substituted styrene suchas o-methylstyrene, p-methylstyrene, m-methylstyrene,2,4-dimethylstyrene, p-ethylstyrene, p-t-butylstyrene, α-methylstyreneor a α-methyl-p-methylstyrene, and an halogenated styrene such aso-chlorostyrene or p-chlorostyrene may also be used. A preferablearomatic vinyl compound includes, for example, styrene, α-methylstyreneand p-methylstyrene, and styrene is especially preferable.

The α,β-unsaturated carboxylic acid may include acrylic acid,methacrylic acid and the like. The α, β-unsaturated carboxylic acidester may include, for example, alkyl acrylates such as methyl acrylate,ethyl acrylate and n-butyl acrylate, alkyl methacrylates such as methylmethacrylate, ethyl methacrylalte and butyl methacrylate, andderivatives thereof. The α, β-unsaturated carboxylic amide may include,for example, acrylamide, methacrylamide, and derivatives thereof. The α,β-unsaturated nitrile may include acrylonitrile, methacrylonitrile,α-chloroacrylonitrile and the like. The vinyl carboxylates may includevinyl acetate, vinyl propionate and the like. The vinyl halide mayinclude vinyl fluoride, vinyl chloride, vinyl bronide, vinyl iodide andthe like. The vinylidene halide may include vinylidene fluoride,vinylidene chloride, vinylidene bromide, vinylidene iodide and the like.The conjugated diene compound may include butadiene, isoprene,chloroprene, piperidene, 1-chlorobutadiene and the like.

There is no special restriction on the radical polymerization initiatorused in the present invention so far as it is capable of initiatingradical polymerization, and the following compounds may be used, forexample: organic peroxides, for example, peroxyketals such as2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane,1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane,1,1-bis(t-butylperoxy)cyclohexane andn-butyl-4,4-bis(t-butylperoxy)valerate, hydroperoxides such as cumenehydroperoxide and diiopropylbenzene peroxide peroxide, dialkylhydroperoxides such as t-butylcumyl peroxide and di-t-butyl peroxide,diacyl peroxides such as lauroyl peroxide and benzoyl peroxide,peroxydicarbonates such as bis(t-butlycyclohexyl) peroxydicarbonate, andperoxyesters such as t-butyl peroxybenzoate, t-butyl peroxyacetate and2,5-dimethyl-2,5-di(benzolyperoxy)hexane; azo compounds such asazoisobutyronitrile, 2,2-azobis(2-methylbutyronitrile), and1,1-azobis(cyclohexane-1-carbonitrile); and peroxides such as benzoylperoxide.

The radical polymerization initiator is preferably used at a mole ratioto vinyl monomer of 0.001/100-10/100 (radical polymerizationinitiator/vinyl monomer), and more preferably at a mole ratio of0.01/100-1/100. This is because, at a ratio of radical initiator tovinyl monomer below 0.001/100it will be difficult to control themolecular weight, and at a mole ratio above 10/100, the polymerizationwill proceed so quickly that it becomes difficult to control thereaction.

There is no special restriction on the process of carrying out thepolymerization of the present invention, and any of the usualpolymerization modes such as bulk polymerization, suspensionpolymerization, bulk-suspension polymerization and solutionpolymerization may be used. In the case of solution polymerization, nomore than 20 parts by weight of solvent may be included in the processwith 100 parts by weight of vinyl monomer, if necessary. Solvent morethan 20 parts by weight is disadvantageous because it will decrease thepolymerization rate and productivity.

There is no special restriction on the solvent included in the processso far as the monomer and the produced polymer are soluble in thesolvent. An example of solvent may be toluene, ethylbenzene, methylethyl ketone, benzene or the like, and toluene or ethylbenzene isespecially preferred because their boiling points are close to thepolymerization temperature. The above solvents may be used alone or incombination.

Furthermore, according to the process of the present invention, themolecular weight can be controlled by the amounts of the initiator andthe monomer as well as the extent of conversion, so that thepolymerization can be conducted in a very simple mode. Furthermore,according to the process of the present invention the molecular weightcan be controlled by the amounts of the initiator and substancerepresented by the above general formula (1) or (2). It is, therefore,very easy to industrialize the present invention. The process accordingto the present invention may be carried out in a continuous mode or inbatch.

The polymerization temperature at which the present invention operatesis typically 60° C.-160° C., and preferably 90° C.-150° C. At atemperature below 60° C., the reaction rate will be too low for anindustrial production process, while at a temperature above 160° C. sidereactions during the polymerization will occur to an extent notnegligible, rendering the reaction control difficult.

When a stricter control is required in carrying out the presentinvention, a compound which has a function controlling heatpolymerization may be used, if necessary. Among the compounds havingsuch a function are, for example, phenylphosphonic acid, D,L-camphor-10-sulfonic acid, p-toluenesulfonic acid,2-fluoro-1-methylpyridinium and the like.

When a thermoplastic resin is produced by the process of the presentinvention, admixtures, stabilizers or the like agents usually used maybe added. For example, in the case of styrene-based thermoplasticresins, a lubricant such as mineral oil, silicone oil, zinc stearate,calcium stearate, or ethylenebisstearylamide, an oxidation inhibitorsuch as a phenolic or phosphorus antioxidant, a UV absorbent, and acolorant may be added during or after the polymerization.

The present invention will be further illustrated by the followingExamples to which the present invention is not restricted.

EXAMPLES

As described below, the polymers of Examples 1-7 and Reference 1-2 weresubjected to the following measurements (1) and (2), and the results aresummarized in Table 1.

(1) Measurement of conversion

The extent of conversion was calculated by gas-chromatographicallyquantifying the amount of remaining monomer in the reaction solutionsampled at a given interval during the reaction.

(2) Measurement of the molecular weight

For the polymer in the reaction solution sampled at a given intervalduring the reaction, the molecular weight was measured according to aGPC method using a GPC (LC-10A) manufactured by SHIMADZU CORPORATION andGPC columns (three KF-806L columns in tandem) manufactured by ShowaDenko K.K.

Unless otherwise indicated, the polymerization reaction was carried outunder nitrogen stream in a polymerization apparatus in which a reactorhaving 20 L inner volume equipped with an agitator was connected to abiaxial extruder equipped with a vent line. The start time of thereaction was defined as the point when the temperature reached 95° C.

Example 1

A stock solution consisting of 150 mol of styrene, 0.3 mol of benzoylperoxide and 0.15 mol of diethylhydroxylamine was introduced into thereactor, and heated with stirring at 95° C. for 3.5 hours. After raisingthe temperature to 130° C., stirring was continued for additional 45hours to synthesize the polymer. After removing remaining monomerpolystyrene was recovered from the biaxial extruder to obtain thepolymer of Example 1.

Example 2

A stock solution consisting of 150 mol of styrene, 0.3 mol of benzoylperoxide and 0.09 of mol diethylhydroxylamine was introduced into thereactor, and polymerized at 95° C. for 3 hours. Then, the polymer ofExample 2 was obtained by following the same procedures as those inExample 1.

Example 3

A stock solution consisting of 150 mol of styrene, 0.3 mol of benzoylperoxide and 0.21 mol of diethylhydroxylamine was introduced into thereactor, and the polymer of Example 3 was then obtained by following thesame procedures as those in Example 1.

Example 4

A stock solution consisting of 150 mol of styrene, 0.3 mol of benzoylperoxide, 0.15 mol of diethylhydroxylamine and 0.3 mol ofcamphorsulfonic acid was introduced into the reactor, and the polymer ofExample 4 was then obtained by following the same procedures as those inExample 1.

Example 5

A stock solution consisting of 150 mol of styrene, 0.3 mol of benzoylperoxide and 0.15 mol of diethylhydroxylaminie was introduced into thereactor, and polymerized at 130° C. for 6 hours. Then, the polymer ofExample 5 was obtained by following the same procedures as those inExample 1.

Example 6

A stock solution consisting of 150 mol of styrene, 0.15 mol of benzoylperoxide and 0.075 mol of diethylhydroxylamine was introduced into thereactor, and the polymer of Example 6 was then obtained by following thesame procedures as those in Example 1.

Example 7

A stock solution consisting of 150 mol of styrene, 0.15 of benzoylperoxide and 0.075 mol of N-hydroxyphthalimide was introduced into thereactor, and the polymer of Example 6 was then obtained by following thesame procedures as those in Example 1.

Reference 1

The polymer of Reference 1 was obtained by following the same proceduresas those in Example 1 with the exceptions that a stock solutionconsisting of 150 mol of styrene and 0.3 mol of benzoyl peroxide wasintroduced into the reactor and that the reaction was stopped after 2hours at 130° C.

Reference 2

The polymer of Reference 2 was obtained by following the same proceduresas those in Example 1 with the exceptions that a stock solutionconsisting of 150 mol of styrene, 0.3 mol of benzoyl peroxide and 0.36mol of 2,2,6,6-tetramethyl-1-piperidinyloxy was introduced into thereactor and that the polymerization time was 80 hours.

Effects of the Invention

As described above, a radically polymerized vinyl polymer having a highmolecular weight and a controlled molecular weight distribution can beobtained by the process of the present invention, even under apolymerization condition at a high temperature. The present inventionprovides, therefore, a process enabling to produce vinyl polymers whichpromise to have practical properties such as appearance, mechanicalproperties and heat resistance useful as materials for various moldingsand coatings. Thus, the industrial and technical value of the presentinvention is extremely high.

Examples/ Reaction Conver- References Time (h) sion (%) Mn × 10⁻⁴ Mw ×10⁻⁴ Mw/Mn Example 1 2 21.0 4.06 6.62 1.63 4 40.4 5.34 7.58 1.41 8 74.67.80 10.45 1.34 Example 2 1 31.2 3.36 5.21 1.55 2 54.6 4.23 6.55 1.55 370.2 5.33 8.04 1.51 Example 3 2 11.7 4.87 7.89 1.62 4 18.2 5.86 9.021.54 6 42.5 7.08 10.55 1.49 8 80.3 8.81 12.51 1.42 Example 4 2 31.6 4.137.31 1.77 4 58.1 5.69 9.39 1.65 8 87.9 6.74 9.77 1.45 Example 5 1 12.42.40 4.82 2.01 3 45.3 5.22 8.87 1.70 6 88.6 7.68 12.60 1.64 Example 6 218.5 6.21 10.43 1.68 4 42.7 12.77 19.66 1.54 8 79.9 17.20 29.58 1.71Reference 1 0.5 54.3 4.75 15.44 3.25 1 70.2 4.44 13.01 2.93 2 89.4 5.2613.26 2.52 Reference 2 20 22.1 0.22 10.50 47.7 40 43.6 0.51 9.77 19.2 8070.5 0.80 11.30 14.1

What is claimed is:
 1. A method of controlling molecular weight of avinyl polymer prepared from a vinyl monomer by radical polymerization ina polymerization system, said process comprising: including in saidpolymerization system an amount of a hydroxylamine sufficient to controlsaid molecular weight of said vinyl polymer, said hydroxylamine having astructure which is a member selected from the group consisting of:

wherein, R₁ and R₂ are members independently selected from the groupconsisting of hydrogen, substituted or unsubstituted aliphatichydrocarbon and substituted or unsubstituted aromatic hydrocarbongroups; and R₃ and R₄ are members independently selected from the groupconsisting of substituted aliphatic hydrocarbon groups.
 2. The methodaccording to claim 1, wherein said radical polymerization is carried outusing a radical polymerization initiator.
 3. The method according toclaim 2 wherein the mole ratio of the radical polymerization initiatorto the vinyl monomer ranges from 0.001/100 to 10/100.
 4. The methodaccording to claim 2 wherein the mole ratio of said hydroxylamine to theradical polymerization initiator ranges from 0.001/1 to 100/1.
 5. Themethod according to claim 1 wherein the vinyl monomer is an aromaticcompound.
 6. The method according to claim 1, wherein said hydroxylamineis a member selected from the group consisting of dimethylhydroxylamine,diethylhydroxylamine, isopropylhydroxylamine, diebenzylhydroxylamine,N-hydroxylaamaleimide, N-hydroxylsuccinimide, and N-hydroxylphthalimide.7. The method according to claim 1, wherein the hydroxylamine is presentin the polymerization system from the beginning of the polymerization.8. The method according to claim 1, wherein said radical polymerizationis carried out by a mode selected from the group consisting of bulkpolymerization, suspension polymerization, and solution polymerization.9. The method according to claim 1 wherein the vinyl monomer is a memberselected from the group consisting of aromatic vinyl compounds, α,β-unsaturated carboxylic acids, α, β-unsaturated carboxylic acid esters,α, β-unsaturated carboxylic amides, α, β-unsaturated nitriles, vinylcarboxylates, vinyl halides, vinylidene halides, conjugated dienes andcombinations thereof.
 10. A method of controlling molecular weightdistribution of a vinyl polymer prepared from a vinyl monomer by radicalpolymerization in a polymerization system, said process comprising:including in said polymerization system an amount of a hydroxylaminesufficient to control said molecular weight distribution of said vinylpolymer, said hydroxylamine having a structure which is a memberselected from the group consisting of:

wherein, R₁ and R₂ are members independently selected from the groupconsisting of hydrogen, substituted or unsubstituted aliphatichydrocarbon and substituted or unsubstituted aromatic hydrocarbongroups; and R₃ and R₄ are members independently selected from the groupconsisting of substituted aliphatic hydrocarbon groups.
 11. The methodaccording to claim 10, wherein said radical polymerization is carriedout using a radical polymerization initiator.
 12. The method accordingto claim 11 wherein the mole ratio of the radical polymerizationinitiator to the vinyl monomer ranges from 0.001/100 to 10/100.
 13. Themethod according to claim 11 wherein the mole ratio of saidhydroxylamine to the radical polymerization initiator ranges from0.001/1 to 100/1.
 14. The method according to claim 10 wherein the vinylmonomer is an aromatic compound.
 15. The method according to claim 10,wherein said hydroxylamine is a member selected from the groupconsisting of dimethylhydroxylamine, diethylhydroxylamine,isopropylhydroxylamine, dibenzylhdroxylamine,N-hydroxylmaleimide,N-hydroxylsuccinimide, and N-hydroxylphthalimide.16. The method according to claim 10, wherein the hydroxylamine ispresent in the polymerization system from the beginning of thepolymerization.
 17. The method according to claim 10, wherein saidradical polymerization is carried out by a mode selected from the groupconsisting of bulk polymerization, suspension polymerization, andsolution polymerization.
 18. The method according to claim 10 whereinthe vinyl monomer is a member selected from the group consisting ofaromatic vinyl compounds, α,β-unsaturated carboxylic acids,α,β-unsaturated carboxylic acid esters, α, β-unsaturated carboxylicamides, α, β-unsaturated nitriles, vinyl carboxylates, vinyl halides,vinylidene halides, conjugated dienes and combinations thereof.
 19. Themethod according to claim 10, wherein said molecular weight distributionis determined by Mw/Mn for said vinyl polymer and Mw/Mn for said polymeris from 1.34 to 2.01.